Adaptation scheme for communications traffic

ABSTRACT

A method of generating a generic framing procedure hierarchy comprising processing a first generic framing procedure frame to determine the overall length of the generic framing procedure frame, mapping the frame into the generic framing procedure payload area of a second generic framing procedure frame at the next level of the generic framing procedure hierarchy, whereby information enabling the size of the generic framing procedure payload remaining after that frame has been extracted is captured in the header fields of the generic framing procedure frame into which the first frame is encapsulated, and wherein the generic framing procedure header indicates whether there are more frames left in the mapping hierarchy when de-encapsulating (i.e., running down) the generic framing procedure frame stack by providing an indicator at level N of the hierarchy that at the level N−1 there is a generic framing procedure frame to extract.

This application is the U.S. national phase of International ApplicationNo. PCT/GB2008/004210 filed 19 Dec. 2008 which designated the U.S. andclaims priority to GB Patent Application No. 0724936.0 filed 20 Dec.2007, U.S. patent application Ser. No. 12/004,080 filed 20 Dec. 2007 towhich the current application is a continuation-in-part of, GB PatentApplication Nos. 0800573.8 filed 14 Jan. 2008, 0800572.0 filed 14 Jan.2008 and 0814056.8 filed 31 Jul. 2008, the entire contents of each ofwhich are hereby incorporated by reference.

The present invention relates to a method of forming a hierarchy ofstacked GFP (Generic Framing Procedure) frames.

In particular, but not exclusively, the GFP hierarchy is capable ofproviding an adaptation layer for the Ethernet communications protocol.The GFP adaptation layer enables a variety of client traffic to becarried across a carrier Ethernet network without requiring each type ofclient traffic to be indicated in the Ethernet frame header.

In particular but not exclusively, the invention relates to a method ofenabling GFP to be carried over GFP so as to separate out the controldomains of different operators of a communications network and/or enableGFP multiplexing.

BACKGROUND

European Patent Application EP 181068 entitled “Method and Device forGeneric Framing Procedure Encapsulation” describes how a plurality ofprotocol data units (PDUs) can be cascaded into a cascaded packet whichis then encapsulated in a GFP frame. A device for GFP encapsulation isalso described which comprises a cascading module for cascading aplurality of PDUs to form a cascade packet and a GFP encapsulationmodule for encapsulating the cascade packet to obtain a GFP packet. Thetechnique proposed by EP 181068 increases the occupation rate of thepayload in a single GFP frame to improve transmission efficiency.

In order to extract a packet from a cascaded packet, however, the entirecascaded packet must be un-cascaded in EP 181068.

United States Published Patent Application US2004/0252720 describes atechnique for providing multiple Fibre Channel (FC) frames in oneframe-mapped GFP transport frame which follows GFP conventions exceptthat a Distributed Delimiter marks each FC frame in the payload of theGFP transport frame.

United States published Patent Application US2005/0169275 describes amethod for transmitting high-level PDUs over low-level protocols, and inparticular describes how Multi-protocol label switching PDUs can betransmitted by adding a pending MPLS PDU to the payload information area(PIA) of a GFP data frame; transmitting the GFP data frame to thedestination node via a transmission network, and retrieving the MPLS PDUfrom the PIA field of the GFP data frame at the destination node.

However, it is desirable to be able to extract a single encapsulatedtraffic unit from a plurality of traffic units which are carried withina carrier GFP frame without requiring all of the other traffic units tobe extracted from the GFP frame.

SUMMARY STATEMENTS OF THE INVENTION

One aspect of the invention seeks to provide a method of adapting clientdata for transportation in a communications system, the methodcomprising:

-   -   receiving a client frame conforming to a generic framing        procedure communications protocol; and    -   mapping the client frame to the payload area of one or more        carrier frames, each carrier frame conforming to a generic        framing procedure communications protocol.

The carrier generic framing procedure frames may be mapped to thepayload area of a protocol data unit of the communications protocol usedby a carrier network of said communications system.

The carrier network communications protocol may comprise an Ethernetcommunications protocol. Alternatively, the carrier networkcommunications protocol comprises an MPLS communications protocol.

A generic framing procedure frame may comprise a header having anextension field arranged to indicate the fragmentation status of itspayload and the sequence number of a payload fragment.

A generic framing procedure frame may comprise a header having anextension field arranged to indicate a channel identity of its payload.

Another aspect of the invention seeks to provide a method of adaptingclient data for transportation in a communications system, the methodcomprising: receiving a client frame conforming to a generic framingprocedure communications protocol; mapping the client frame to thepayload area of a plurality of carrier frames, each carrier frameconforming to a generic framing procedure communications protocol andhaving an extension field arranged to indicate the fragmentation statusof its payload and the sequence number of a payload fragment.

A method of reassembling a client from fragmented data transported overa communications system, the method comprising: receiving a plurality ofcarrier frames conforming to a generic framing procedure communicationsprotocol; processing an extension field of a header of each of theplurality of carrier frames to determine if it indicates thefragmentation status of its payload and the sequence number of a payloadfragment; if a plurality of fragments of the same client frame aredetected, processing the plurality of frames to extract each payloadfragment; reassembling the client frame from said payload fragments.

The method may be implemented on a node in the communications networkarranged to provide an aggregation service to multiplex client trafficreceived from lower rate ports to a carrier network accessed through oneor more higher rate ports of the node, the method comprising: receivinga plurality of client frames from a plurality of lower rate ports,mapping the client traffic into the payload area of one or more of saidclient generic framing procedure communications protocol frames; whereinwhen mapping each client generic framing procedure frame to the payloadinformation area of a carrier frame, each carrier frame conforming to ageneric framing procedure communications protocol has an extension fieldarranged to indicate the channel number of its payload, and wherein eachcarrier generic framing procedure frame is mapped to the payload area ofa protocol data unit of the carrier network communications protocol.

The method may be arranged to provide an aggregation service tomultiplex traffic from lower rate ports to higher rate ports, the methodcomprising: receiving a plurality of client frames conforming to ageneric framing procedure communications protocol from a plurality oflower rate ports; mapping each client frame to the payload informationarea of a carrier frame, each carrier frame conforming to a genericframing procedure communications protocol and having an extension fieldarranged to indicate the channel number of its payload.

Another aspect of the invention seeks to provide a method of generatinga generic framing procedure hierarchy comprising: processing a firstgeneric framing procedure frame to determine the overall length of thegeneric framing procedure frame; mapping the frame into the genericframing procedure payload area of a second generic framing procedureframe at the next level of the generic framing procedure hierarchy,whereby information enabling the size of the generic framing procedurepayload remaining after that frame has been extracted is captured in oneor more of the fields in the header of the generic framing procedureframe into which the first frame is encapsulated.

The generic framing procedure header indicator may indicate whetherthere are more frames left in the mapping hierarchy whende-encapsulating the generic framing procedure frame stack.

The header indicator may provide an indicator at level N of thehierarchy that at the N−1 level there is a generic framing procedureframe to extract.

Another indicator in the payload header may indicate that there are nomore generic framing procedure frames to extract and the hierarchy ofgeneric framing procedure frames is terminated.

Another aspect of the invention seeks to provide a method of restoringclient data which has been adapted for transportation in acommunications system using any of the above methods, the methodcomprising: processing at a node in said communications system areceived frame to determine if its payload comprises a frame conformingto a generic framing procedure communications protocol; and if thepayload is a generic framing procedure communications protocol frame:

-   -   i) de-encapsulating the payload;    -   ii) processing the header fields of the de-encapsulated generic        framing procedure frame; and    -   iii) determining if the payload further comprises one or more        generic framing procedure communications protocol frames, and if        so,    -   repeating the above steps i) to iii).

The method may further comprise:

-   -   processing one or more extension fields of a header of each        de-encapsulated generic framing procedure frame to determine if        a channel identifier is present indicating the channel identity        of the client signal from which the payload is derived.

The method may further comprise:

-   -   processing one or more extension fields of a header of each        generic framing procedure frame to determine if one or more        values of said extension fields are present which indicate the        fragmentation status of its payload and the sequence number of a        payload fragment.

The method may further comprise, if a plurality of fragments of the sameclient frame are detected:

-   -   processing the plurality of frames to extract each payload        fragment;    -   reassembling the original payload from said payload fragments.

Another aspect of the invention seeks to provide apparatus comprisingone or more components arranged to implement steps in any of the abovemethod aspects.

One aspect of the invention seeks to provide apparatus comprising:

-   -   a processor arranged to process a first generic framing        procedure frame to determine the overall length of the generic        framing procedure frame;    -   a mapper arranged to encapsulate the first frame into the        generic framing procedure payload area of a second generic        framing procedure frame at the next level of the generic framing        procedure hierarchy,    -   whereby information enabling the size of the generic framing        procedure payload remaining after that frame has been extracted        is captured in the header fields of the generic framing        procedure frame into which the first frame is encapsulated.

The generic framing procedure header indicator indicates whether thereare more frames left in the mapping hierarchy when de-encapsulating thegeneric framing procedure frame stack.

One aspect of the invention seeks to provide a method of generating ageneric framing procedure hierarchy comprising:

-   -   processing a first generic framing procedure frame to determine        the overall length of the generic framing procedure frame; and    -   mapping the frame into the generic framing procedure payload        area of a second generic framing procedure frame at the next        level of the generic framing procedure hierarchy,    -   wherein information enabling the size of the generic framing        procedure payload remaining after that frame has been extracted        is captured in the header fields of the generic framing        procedure frame into which the first frame is encapsulated.

The generic framing procedure header may indicate whether there are moreframes left in the mapping hierarchy when de-encapsulating the genericframing procedure frame stack by providing an indicator at each level ofthe stack hierarchy if at the lower level of the stack there is ageneric framing procedure frame to extract.

Another aspect of the invention seeks to provide a method of generatinga generic framing procedure hierarchy comprising:

-   -   processing a first generic framing procedure frame to determine        the overall length of the generic framing procedure frame;    -   mapping the frame into the generic framing procedure payload        area of a second generic framing procedure frame at the next        level of the generic framing procedure hierarchy,    -   whereby information enabling the size of the generic framing        procedure payload remaining after that frame has been extracted        is captured in the header fields of the generic framing        procedure frame into which the first frame is encapsulated, and        wherein the generic framing procedure header indicator indicates        whether there are more frames left in the mapping hierarchy when        de-encapsulating the generic framing procedure frame stack by        providing an indicator at level N of the hierarchy that at the        N−1 level there is a generic framing procedure frame to extract.        The de-encapsulation process comprising running down the generic        framing procedure frame stack.

In one embodiment, another indicator in the payload header indicatesthat there are no more generic framing procedure frames to extract andthe hierarchy of generic framing procedure frames is terminated.

Another aspect of the invention seeks to provide apparatus arranged toimplement the method aspect, the apparatus comprising:

-   -   a processor arranged to process a first generic framing        procedure frame to determine the overall length of the generic        framing procedure frame;    -   a mapper arranged to encapsulate the first frame into the        generic framing procedure payload area of a second generic        framing procedure frame at the next level of the generic framing        procedure hierarchy,    -   whereby information enabling the size of the generic framing        procedure payload remaining after that frame has been extracted        is captured in the header fields of the generic framing        procedure frame into which the first frame is encapsulated, and        wherein the generic framing procedure header indicator indicates        whether there are more frames left in the mapping hierarchy when        de-encapsulating (i.e., running down) the generic framing        procedure frame stack by providing an indicator at level N of        the hierarchy that at the N−1 level there is a generic framing        procedure frame to extract.

One aspect of the invention seeks to provide an adaptation layer for acarrier network service which enables a plurality of client trafficunits (for example, protocol data units (PDUs) to be encapsulated withina single adaptation layer traffic unit, which is in turn encapsulatedwithin the payload area (also referred to as a service data unit) of thecarrier network.

When a network node receives a carrier PDU, it is able to process thePDU header to determine if the payload area of the carrier protocol dataunit includes an adaptation layer signal. If an adaptation layer signalaccording to an embodiment of the invention is present it is processedand this enables the position of each client signal PDU encapsulatedwithin the adaptation layer signal payload. This enables an individualclient PDU to be extracted from the adaptation payload area within thecarrier frame payload area without requiring any of the other clientPDUs carried within the same carrier frame payload area to be extractedas well. This enables a carrier frame to carry a variety of clientsignals in a more versatile manner than is known in the art.

Aspects of the present invention are as set out above and in theaccompanying claims, and the preferred embodiments are as set out aboveand by the accompanying dependent claims.

Those of ordinary skill in the art will find it apparent that theinvention may comprise any appropriate combination of the aspects andpreferred embodiments as set out herein and in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the invention will now be discussed withreference to the accompanying drawings which are by way of example onlyand in which:

FIG. 1 shows schematically in more detail a standard GFP frame format;

FIG. 2A shows schematically the hierarchical levels of a GFP frame stackaccording to an embodiment of the invention;

FIG. 2B shows schematically the hierarchical levels of a GFP frame stackshown in FIG. 2A for comparison with FIG. 2C;

FIG. 2C shows schematically the hierarchical levels of a GFP frame stackwhere the client end of the stack includes a plurality of GFP framesaccording to an embodiment of the invention;

FIG. 2D shows schematically a three-level hierarchy GFP frame stackwhere the intermediate level and client end of the stack includes aplurality of GFP frames according to an embodiment of the invention;

FIG. 2E shows how a frame at level N can be fragmented into a pluralityof frames according to an embodiment of the invention;

FIG. 3 shows schematically the GFP stack in more detail according to anembodiment of the invention;

FIG. 4 shows a GFP header extension field according to an embodiment ofthe invention which provides a data transport scheme which fragmentsclient traffic;

FIG. 5A shows a GFP header extension field according to an embodiment ofthe invention which provides a data transport scheme for multiplexingGFP client traffic;

FIG. 5B shows a GFP header extension field according to an embodiment ofthe invention which provides a data transport scheme for multiplexingand fragmenting client traffic;

FIG. 6 shows schematically how a plurality of client GFP channels aremultiplexed into a single carrier GFP data channel according to anembodiment of the invention;

FIG. 7 shows schematically how an unfragmented client GFP data frame isfragmented into a plurality of carrier GFP frames according to anembodiment of the invention;

FIG. 8A shows schematically an encapsulating node according to anembodiment of the invention;

FIG. 8B shows schematically a de-encapsulating node according to anembodiment of the invention;

FIG. 9A shows steps in a method of encapsulating client according to anembodiment of the invention; and

FIG. 9B shows steps in a method of de-encapsulating the payload of acarrier frame according to an embodiment of the invention.

DETAILED DESCRIPTION OF PRESENT EXAMPLE EMBODIMENTS

The best mode of the invention will now be described. Those of ordinaryskill in the art will be aware that the description of the invention hasbeen simplified for clarity and may omit to refer explicitly to featureswhich are apparent and already known to those of ordinary skill in theart as essential for its implementation, such features being implicitlyincluded in the description of the invention. The description may alsoomit to mention alternative features which are functionally equivalentto the features recited herein.

FIG. 1 of the accompanying drawings shows a GFP frame format as known inthe art, which can be modified for use as an adaptation layer accordingto an embodiment of the invention. The GFP frame format has the featuresof the protocol as defined in the G.7041 standard established by theInternational Telecommunications Union Telecommunicationsstandardisation sector (ITU-T), the contents of which are herebyincorporated by reference.

Those of ordinary skill in the art will be aware that the GFP protocolwas intended as a universal mapping mechanism for packets into TDMtechnologies. GFP supports multiple protocols and is extensible. Thepreferred embodiment of the invention uses frame-based GFP, but inalternative embodiments of the invention, transparent GFP (GFP-T) isused. GFP-T is an extension to GFP developed to provide efficientlow-latency support for high-speed WAN applications including storagearea networks. Rather than handling data on a frame-by-frame(packet-by-packet) basis, GFP-T handles block-coded (e.g., 8B/10B)character streams.

In one embodiment of the invention, a hierarchical GFP mapping schemeprovides an adaptation layer for an Ethernet carrier network service.The hierarchical GFP mapping scheme adaptation layer enables a pluralityof client signals to be carried within an Ethernet frame, as describedherein-below and, for example, as described in the applicants co-pendingpatent application entitled “CLIENT/SERVER ADAPTATION SCHEME FORCOMMUNICATIONS TRAFFIC which claims priority inter alia fromGB0724936.0, the full contents of which are hereby incorporated byreference.

As shown schematically in FIG. 1 the structure of a GFP client framecomprises a core header, a payload header, an optional extension header,and an optional payload frame check sequence (FCS). Those of ordinaryskill in the art will be aware that fields of the GFP frame which arenot relevant in the present context may be omitted for clarity from thediagrams and description below.

The Core Header has a field that has an indication for the payloadlength which is a 2-byte (8 octet bit) field indicating how many bytes(bit octets) are in the GFP payload area. By subtracting the subsequentpayload header and any optionally present payload FCS overhead from thepayload area, the payload length value also indicates the size of thetrue client payload information. The Payload Header is a variable lengtharea and comprises two mandatory fields and optionally, some extensionheaders. The two mandatory types of fields are the Payload type fieldsof which the Payload Type Most Significant Byte (MSB) and Payload TypeLeast Significant Byte (LSB) are shown in FIG. 1 and the header errorcorrection (HEC) fields of which the Type HEC MSB and Type HEC LSB areshown in FIG. 1.

The Payload Type field has multiple subfields. The Payload TypeIdentifier (PTI) identifies the type of frame and may take two values:user data frames and client management frames. The Payload FCS Indicator(PFI) subfield indicates if there is a payload FCS. The Extension HeaderIndicator (EXI) subfield indicates the type of extension header in theGFP frame. Three types of type extension headers are known in the art, anull extension header, a linear extension header for point-to-pointnetworks, and a ring extension header for ring networks. Also shown isthe User Payload Identifier (UPI) subfield which identifies the type ofpayload in the GFP frame. The UPI is set according to the transportedclient signal type, of which several defined values already exist forcommunication protocols such as Ethernet, PPP, IP, MPLS, Fibre Channel,FICON, ESCON, and Gigabit Ethernet.

The Payload Information Field contains the client data. Two modes ofclient adaptation are defined for GFP as mentioned hereinabove,frame-mapped GFP and transparent-mapped GFP. Frame-mapped GFP payloadsconsist of variable length packets and one client frame is mapped in itsentirety to one GFP frame. In transparent mapped GFP, a number of clientdata characters (mapped into block codes) are carried within a GFPframe.

A hierarchical GFP mapping is implemented using the PTI, EXI, and UPIfields according to an embodiment of the invention.

FIGS. 2A, 2B, 2C, 2D and 2E and 3 show schematically how one or more GFPframes can be mapped inside another GFP frame. The mapping process isrepeatable to create a hierarchy provided that at each level the mappingis always into a bigger frame in the next level of the hierarchy. Ifnot, then a frame is fragmented into a plurality of small segments whichare mapped into a plurality of frames.

As shown in FIGS. 2A and 2B, each GFP frame is stacked within thepayload of the GFP frame at a lower level of the hierarchy. As shown inthe embodiment of FIGS. 1 and 2A, the payload of each GFP frame at ahigher level than the first level (where the payload will compriseclient data) comprises the contents of another GFP frame. The lower thelevel of the GFP hierarchy, the closer the level is to the client layer.In some embodiments of the invention, the client layer may have a higherlevel than GFP in the Open Systems Interconnection communicationsprotocol stack, but in other embodiments of the invention this need notbe the case. For example, a client level can comprise GFP again orInternet Protocol or Asynchronous Transfer Mode to name a few clientlayer communications protocols for embodiments of the invention.Similarly, the higher the level of the GFP hierarchy, the closer thehierarchy level is to a carrier (or equivalently server) layer. Thehighest level of frames in the GFP hierarchy will be mapped to thepayload of frames in a carrier network in a 1:1 manner, so that thepayload in each of highest level frames (level N in FIG. 2B) is thenmapped to the payload of a frame conforming to the communicationsprotocol of a network which is offering a carrier service to the networkfrom which the client signals originated. In some embodiments of theinvention the carrier (equivalently server) network has a lower level ofcommunications protocol than GFP in the OSI communications protocolstack, but this is not the case in other embodiments of the invention.For example, a carrier network may use one of the GFP, or Ethernet, orMPLS, or ATM communications protocols and variants thereof to name but afew possible carrier network transport technologies.

FIG. 2C shows how within a single level of the GFP hierarchy it ispossible to have a plurality of GFP frames concatenated together. InFIG. 2C, at level N−1 two GFP frames are placed in the payload area of asingle GFP frame at a lower level of the hierarchy. The level N−1 framescarry the same client signal in FIG. 2C, but alternatively, the payloadof some of the N−1 level frames could originate from one or moredifferent client signals in other embodiments of the invention. Inanother embodiment of the invention, two or more level N−1 frames carryfragments of the same client frame (or alternatively a level N−2frame—see FIG. 2D) in which case their headers will also include afragmentation indicator and sequence information.

FIG. 2D shows schematically a three level GFP hierarchy in which atlevel 1 four frames are concatenated together within the payload of asingle frame at level 2 of the frame hierarchy. The payload of each ofthe level 2 frames is able to have an internal data structure which isindependent of the internal data structure of any other frames alsomapped into the payload of the level 3 GFP frame. As shown in FIG. 2D,therefore, the left-hand side level 2 frame has a payload containingfour level 1 frames. The right-hand side level 2 frame has no additionalinternal data structure apart from client data. Both level 2 frames aremapped into the payload area of the level 1 GFP frame. The level 1 GFPframe can then be mapped to the payload area of a carrier network PDUfor transportation over a carrier network.

FIG. 2E shows how in an embodiment of the invention a GFP frame at anylevel of the GFP hierarchy is able to be fragmented into a number of GFPframes which occupy the same level of the GFP hierarchy. Each GFP frameheader is modified to indicate it has a fragmented payload and isprovided with a sequence indicator in its extension field, as isdescribed in more detail later herein below. This enables a clientsignal having a large PDU or data structure to be first mapped to a GFPframe which is then fragmented into a plurality of smaller GFP frames.The smaller GFP frames can then be mapped to an equal number of carriernetwork frames.

FIG. 3 shows how information from one level of the GFP frame stack iscarried by the GFP frame at the next level of the GFP stack. As shown inFIG. 3, the PDU Length Indicator for a GFP frame at a first level isprocessed to determine how may bit octets (i.e., bytes) will taken up bythe encapsulated field being mapped into the GFP payload area at thenext level of the hierarchy. This information enables the extraction ofthe encapsulated protocol data unit for the client traffic signal (whichin the embodiment of the invention shown in FIGS. 2 and 3 is another GFPframe) as it allows the size of the GFP payload remaining after thatframe has been extracted to be determined during the “de-mapping”process. It also enables any node receiving the signal to determine ifthere are other GFP frames remaining in the payload area tode-encapsulate. For example, in FIG. 2C, after de-encapsulating thefirst level N−1 frame from the level N frame payload area, if the entirelength of the level N frame payload has not been de-encapsulated, thenode performing the de-encapsulation will continue to process the bitstream received on the basis that another N−1 level GFP frame is withinthe N level GFP payload area.

In addition, the Payload header information of the GFP frameencapsulating the other GFP frame indicates what is being carried andwhether it is a GFP frame or something else. To implement thehierarchical GFP mapping, the GFP header indicator indicates whetherthere are more frames left in the mapping hierarchy whende-encapsulating (i.e., running down) the GFP frame stack. An indicatorprovided in the header of a GFP frame at level N of a frame stackhierarchy indicates that the de-encapsulation process is to bere-iterated to de-encapsulate the GFP frames from within the payload ofthe GFP frame that has just been de-encapsulated, i.e., that at the nextlevel there are one or more GFP frames to extract. Any other indicatorin the payload header indicates that there are no more GFP frames toextract and the hierarchy of GFP frames is terminated. In one embodimentof the invention, where data from a client communications network (forexample, a Local Area Network or LAN) is to be transported over acarrier communications network (for example, a Wide Area Network or WAN)which is using a GFP mapping scheme according to the invention as anadaptation protocol, the payload of the frames in the lowest level ofthe GFP hierarchy comprises data conforming to a communications protocolsupported by the client network.

In one embodiment of the invention, GFP traffic generated in a firstnetwork domain is encapsulated within GFP provided by another networkdomain. This enables traffic provided by a first carrier network to becarried over the network of a second carrier in a transparent mannerwithout requiring a instance of a common control plane.

It is common for GFP to have proprietary extensions and/or mappingswhich would otherwise cause problems as traffic crosses over networkdomains. In one embodiment of the invention the requirement to alwaysexamine the client traffic at each boundary node between network domainsis removed as the GFP protocol stack isolates the proprietary fields ofone network domain by carrying them at the next frame level in the GFPframe hierarchy, thus encapsulating the proprietary fields with a GFPframe payload area over the other network domain.

Other embodiments of the invention enable segmentation of client frameswithin the carrier network as well as concatenation of a plurality ofGFP frames (whether they individually carry segments from the sameclient frame or not providing they can be routing in common over atleast part of the carrier network) within another GFP frame which canthen be mapped into the carrier frame payload area.

Thus embodiments of the invention provide a data transport scheme inwhich the payload header and/or the optional extension header areadapted to enable client frames to be carried within carrier frames andeverything else can be treated in the normal manner as described in thevarious GFP standards, such as G.7041 for example, whose contents areincorporated herein by reference.

In one embodiment of the invention, the GFP stack is arranged to enableGFP frame-by-frame multiplexing which is described in more detailhereinbelow. Another embodiment of the invention uses the GFP extensionheader of a GFP frame to indicate segmentation or concatenation of theGFP frames carried in its the payload.

In these embodiments, the term “carrier” GFP frame indicates the framewithin whose payload part or all of a client GFP frame is encapsulated,the term “client” indicating the encapsulated frame or frame fragment,i.e., the relation of each frame within the frame hierarchy. Thus in athree tier hierarchy a frame in the middle layer is a carrier to thefirst layer and a client of the third layer. Each GFP frame whetherclient or carrier conforms to the standard GFP communications protocols(e.g. GFP-T, GFP-F, and other variants) and so comprises: a core header,a payload header, a payload area, an optional extension header, and anoptional payload Frame Check Sequence. In practice, in many embodimentsof the invention, the “client” GFP will itself contain data derived froma client signal and the carrier GFP frame is mapped to the payload orservice data unit of a PDU of a carrier network.

A carrier GFP frame has a payload header which is 4-64 bytes long andcomprises: a 2 byte type field which is used to implement the invention,a 2 byte header error control (HEC) that ensure integrity of the typefield known as the tHEC (which is used in its standard form), anoptional extension header which is 0 to 58 bytes long, and an optional 2byte header error control (HEC) that ensures that the integrity of theoptional extension header and is known as the eHEC (if present this isused in a standard form).

The presence of a GFP frame which is encapsulated in the payload of aGFP frame is indicated in the carrier GFP frame by the GFP type field inthe payload header and/or the optional extension header.

The payload header supports data link management procedures specific tothe client signal being carried (in other words the payload). Thepayload headers type field is subdivided into a number of fields asfollows:

-   i) A 3 bit payload type identifier (PTI). This identifies the type    of GFP client frames. Currently the following are defined: 000 that    identifies the frames as being client data (user data frames), 100    for client management frames and other values are reserved for    further study. A GFP client data frame is used to transport data    from the client signal. The GFP Client Management Frames are used to    transport information associated with the management of the client    signal or GFP connection.-   ii) A 1 bit payload FCS (frame check sequence) indicator (PFI). This    indicates the presence (set to 1) or absence (set to 0) of the    payload FCS field.-   iii) A 4 bit extension header indicator.-   iv) An 8 bit user payload identifier (UPI) is used to indicate the    type of payload carried in the GFP payload information field.

One embodiment of a method of transporting data according to theinvention sets the type field and its subfields to a set of values. Inthis embodiment, the client data is transported over GFP using theclient data frames. These frames are GFP client frames consisting of aCore Header and a Payload Area. The Type field of the client data framesis then set as follows

-   -   PTI=000,    -   PFI=Payload specific.    -   EXI=Payload specific.    -   UPI=Payload specific.

Whether Frame Check Sequence (FCS) is enabled or not will determine thevalue that the Payload FCS Indicator (PFI) is set to 1 or 0. The UPIindicates what the client payload is. For example frame mapped Ethernethas a UPI set to 0000 0001. Currently 0001 0011 through to 1110 1111 arereserved for future standardization. So to transport GFP-F over GFP-F itis sufficient to choose either a value reserved for proprietary use(1111 0000 to 1111 1110) or an unallocated value and assign it torepresent frame mapped GFP, if instead the GFP client is GFP-T and thecarrier service is GFP-F, at least another UPI is required.

The payload Extension Header is intended to support technology specificdata link headers such as virtual link identifiers, source/destinationaddresses, port numbers, Class of Service, extension header errorcontrol, etc. The type of the extension header is determined by thecontent of the EXI bits. Those of ordinary skill in the art will beaware that at the date of the invention three Extension Header variantsare defined as follows:

When EXI=0000 the extension header is null. In this case there is noseparate extension header and no eHEC. This applies to the case of apoint-to-point scenario where it is intended that the transport path isdedicated to one client signal. In such an embodiment, a transportscheme with a two-level GFP frame hierarchy comprises a single GFPstream being supported by the encapsulating GFP. This could for exampleoccur to allow traffic on an incoming port to be encapsulated fortransport on an outgoing port in a point-to-point configuration. In suchan embodiment, the carrier GFP frame headers will have an EXI=0000 valuein the extension field if there is no fragmentation.

When EXI=0001 the extension header is a linear header. It is intendedfor applications that are linear (i.e, point-to point) and requireaggregation of the client signals using the adaptation layer. This isused in embodiments of the invention to indicate GFP multiplexing in thedata transport scheme, where more than one client GFP signal issupported by the encapsulating GFP. In this case, the original typefield of the carrier GFP headers now comprises:

-   -   PTI=000;    -   PFI=0 or 1;    -   EXI=0001;    -   UPI=Payload specific.

In one embodiment, a carrier GFP (level 2 frame) payload has a lengthlimit of N octets. There are M GFP encapsulated client frames (level 1frame), each of N octets. If a 1:1 mapping is implemented between thecarrier (N=2) payload and the client GFP (N=1) frame traffic, then eachcarrier (level 2) GFP frame's payload carries a single client GFP frame(level 1). In total, M carrier GFP frames will be required to carry theM client signals. If, however, frame sharing is required, for example ifa single carrier GFP frame is shared between multiple client frames,i.e., a M:1 client to carrier mapping is implemented, then each carrierframe payload carries M different client payload fragments with eachclient payload fragment comprising N/M octets. In total however, Mcarrier frames are still required to send each client N octets (see alsoFIG. 7 described herein below).

In this case, if the GFP frame is being mapped to a payload informationarea which is larger than the maximum size of the payload area then someform of segmentation and reassembly mechanism needs to be provided.

This is provided in one embodiment of a data transport scheme accordingto the invention by providing a new extension header for the carrier GFPframe. In this embodiment, the communications system is considered to bepoint to point and there is no multiplexing of multiple streams. Thedata transport scheme maps a stream where some of its frames (but notnecessarily all) have a larger size than the encapsulating payload area.If all the client frames are smaller, then of course this type ofextension header is not required to implement the invention.

In this case, an EXI value needs to be defined which can be a valuetaken from one of the currently unused extension headers. The extensionheader provided has a spare field and a header error check and nowcomprises 4 bytes of data and provides a means of identifying if anencapsulated frame has been fragmented, if it is the first, middle orlast fragment, and provides a sequence number.

FIG. 4 shows in more detail an exemplary internal structure of such aGFP extension header according to the invention. In FIG. 4, the 4 byteheader field is segmented into an 8 bit extension Header Error CheckLeast Significant Byte (eHEC LSB) field, an 8 bit extension Header ErrorCheck Most Significant Byte (eHEC MSB) field, a spare 8 bit extensionheader field, a 6 bit Sequence Number field, and two single bit fields,the E-field and the B-field. The E-field and B-field shown aresufficient to indicate what is happening with the fragmentation processor in other words the fragmentation state of the payload. The sequencenumber indicates the order of the fragments to aid their reassembly whenrecovered from the carrier service. For example, one could configureE=1, and B=1 to indicate the start of a series of fragments, E=0, B=1 toindicate the end of a series of fragments, and E=1, B=0 to indicate afragment somewhere in the middle (which would require the sequencenumber to indicate its correct position), and E=0, B=0 to indicate thatno fragmentation is present.

FIGS. 5 a and 5 b both show how a GFP-type extension header isconfigured in one embodiment of the invention which implements amultiplexing scheme which requires a a channel identifier to beprovided. The header in FIG. 5 a comprises a CID field or Channel IDfield which is one byte long and can therefore identify 256 differentcommunications channels between GFP In the embodiment of the inventionshown in FIG. 5A a spare byte is shown in the extension header which isnot used but which is used in the embodiment of the invention shown inFIG. 5B where the spare byte is used to support the fragmentation ofclient frames.

Embodiments of the invention use the CID field of a GFP frame tomultiplex multiple GFP sessions, each session being identified by a GFPframe having a CID with a different value. A GFP frame header is 8 byteslong and the payload area is approx 65000 bytes long, it is possible tohave multiple GFP sessions multiplexed in an encapsulating GFP frame.The maximum number of sessions which can be multiplexed in this way is256 although in practice the number is likely to be much smaller than256, with the practical limit on the number of sessions which can bemultiplexed in this way depending on the length of the encapsulatedframes being smaller than the length of the encapsulating GFP framespayload information field. By using a CID value and a predetermined UPIin one embodiment of the invention multiple GFP sessions can be carriedin the same GFP frame. This enables client traffic to be multiplexedfrom lower rate ports onto a higher rate port to provide apoint-to-point aggregated service.

FIG. 6 shows in more detail how two channels of client frames are mappedto the payload of a carrier channel. In FIG. 6, client frames n, n+1,n+2, and n+3 from channel 0 are shown on the left and client frames n,n+1, n+2, n+3 from channel 1 are shown on the right. Each frame is firstmapped to the payload information of a GFP frame, which together withthe payload header, extension header and FCS is then mapped to thepayload area of the carrier GFP frame. Each client frame is mapped usingan extension header such as that shown in FIG. 5A or 5B, i.e., onecomprising a channel identifier (CID) value which identifies the payloadof the encapsulating GFP frame is associated with a particular channel.In this case, channel 1 is mapped with a CID value which identifies thepayload of the carrier GFP frame is associated with channel 1. Channel 2is similarly mapped using an extension header comprising a CID valuewhich identifies payload associated with channel 2.

In FIG. 6 time flows horizontally in the direction of the arrow at thebottom for the carrier stream and the frames are mapped 1:1 so that inthe horizontal flow of frames shown the first frame in the left is fromChannel 0, the next is from Channel 1, the next from Channel 0 again.The CID then simply identifies what channel a frame belongs to. If theclient GFP frames are smaller or equal to the than the payloadinformation area, then an Extension header having the form shown in FIG.5A can be used. However, if not, then additional information needs to becaptured as described herein above and an extension field such as thatshown in FIG. 5B can be used.

The multiplexing process used to map the client frames into payloadinformation and then into the payload area of a stream of GFP carrierframes can be any known multiplexing process known to one of ordinaryskill in the art as apparently suitable for this purpose, and similarlythe demultiplexing process can be implemented using a knowndemultiplexing process suitably adapted for the purposes of theinvention.

FIG. 7 shows how frame fragmentation occurs. In FIG. 7 an unfragmentedGFP frame comprising X bytes of payload is split into a series of X/nbytes of payload fragments. In FIG. 7, the first fragment of X/n byteswill be carried in a first GFP carrier frame, and all other carrier GFPframes will carry the same size of fragment except for the last carrierGFP frame, which carries the remainder of the payload. So if X=10, andX/n=2 bytes, each of the 5 carrier GFP frames each carry 2 bytes.However, if X=11, and X/n=2 bytes, then the last (6^(th)) carrier GFPframe will carry 1 byte.

The invention can be used in a variety of networking scenarios. Forexample, one embodiment of the invention enables a data transport schemeto be implemented in a communications system comprising a single networkand GFP carrier service. Here GFP transport apparatus (for example, linecards) are provided at the edge of the network (for example, in thefirst and last Synchronous Digital Hierarchy Cross-Connects). The GFPframing appears only at the edge of the location, i.e., at these points,which removes the need to perform any processing within the network.

In another embodiment of the invention a data transport scheme isimplemented in a communications system comprising a second GFP carrierwhich offers a service to the first GFP carrier. Now there are three GFPhops within the communications network, firstly a hop in/out of GFP atthe edge and also in the middle between the two GFP carrier services. IfGFP-T is performed on the first and last hops and GFP-F is performed inthe middle, then as there is more information being transported in eachGFP-T frame (as GFP-T supports line codes that include interframe gapsand preamble and frames) than in each GFP-F frame. To map the line codeinformation over, a data transport scheme such as that shown in FIG. 7can be implemented which fragments a larger GFP-T frame into a pluralityof GFP-F frames. Similarly, if the mapping is proprietary on the 1^(st)and 3^(rd) hop in the network, then in the intermediate hoe theproprietary mapping needs to be maintained which can again be achievedusing a data transport scheme according to the invention whichimplements GFP-in-GFP, i.e., hierarchical or fragmented GFP.

In one embodiment, a communications system uses GFP as an interface to aline system which is not supported underneath by a TDM communicationsprotocol. In this embodiment, a carrier GFP service would have GFPtraffic which is processed on each hop in the communications network.All proprietary client GFP traffic is then transported transparentlyover the network by implementing the data transport scheme according toan embodiment of the invention.

FIGS. 8A and 8B show schematically some of the functional componentsrequired in boundary nodes 10, 22 respectively between a client network(not shown) and a carrier network (not shown) to implement an embodimentof the invention in a communications system. FIGS. 8A and 8B have beengreatly simplified. Components which a person of ordinary skill in theart would find apparent as necessary to implement an adaptation schemeaccording to an embodiment the invention have been omitted for clarity.The components shown in the figures and described below are forexemplary purposes. In other embodiments they may be removed, combinedor substituted for by functional equivalents as are known to persons ofordinary skill in the art.

FIG. 9A shows steps in an embodiment of the invention in which a nodesuch as that shown in FIG. 8A encapsulates client signal data within acarrier frame data structure for transmission over a carrier network.

FIG. 9B shows steps in an embodiment of the invention in which a nodesuch as that shown in FIG. 8B de-encapsulates client signal data fromwithin a carrier frame data structure for transmission over a clientnetwork.

In FIG. 8A, node 10 functions as a point of encapsulation for clienttraffic. The receiver 12 of node 10 receives a client traffic signal(step 40 shown in FIG. 9A). Each received client traffic unit is thenprocessed by data processor 14 to determine from its data structure iffragmentation is required (step 42). The processing determines one ormore characteristics of the client signal required to map the clientsignal into one or more GFP adaptation layer frames, for example, thetype of client signal communications protocol if this is not the samefor all traffic received: the size of the client signal protocol dataunit (PDU) and/or SDU routing information etc.

If no fragmentation is required, the entire client PDU is mapped to thepayload of the GFP adaptation layer. If the total amount of client datato be mapped to each payload area of a GFP adaptation layer frame islarger than a predetermined amount, for example, an amount which in oneembodiment depends on the maximum size of payload supportable by thecarrier network PDU which is determined by the size of the service dataunit (SDU) of the communications protocol for the carrier network, thenthe client signal payload is fragmented by data fragmentor 16.

If fragmentation is not required, then the client signal PDU is passedby the data processor 14 directly to the data mapper 18 forencapsulation within the payload area of a GFP frame, and a suitable GFPheader is generated. If a plurality of different client signals (forexample, client channels or data streams) are to be mapped to a singlecarrier channel signal for transmission in the carrier network, theneach GFP frame will include in its header an indication of the clientchannel from which its payload was derived.

The GFP frame encapsulating the client signal is then in turnencapsulated by the data mapper 18 either within a carrier GFP framewhich is then mapped to the payload area of a PDU for a carrier networkfor transmission by an appropriate transmitter over the carrier network,or directly into the payload area of the carrier PDU. In this way, wherethe carrier network is Ethernet, the carrier Ethernet frames are onlyrequired to include a GFP Ethertype regardless of the type ofcommunications protocol that the client signal has.

Where fragmentation is to occur, the data forming each client PDUpayload fragment is re-structured (step 44). For each client PDUreceived by mapper 18, the client payload (equivalently client SDU) ismapped along with a copy of the client frame header to the payload of afirst level GFP frame and the communications protocol type of the clientsignal and/or sequence and/or fragmentation data is written to theextension field(s) of the header of that first level GFP frame (steps 46and 48) in FIG. 9A and as described hereinabove with reference to FIG.5B). The payload length indicator of the first level GFP frame is alsogenerated.

In one embodiment of the invention, other information required to routethe client signal over the carrier network is extracted for use ingenerating the carrier frame header information.

If more than one first level GFP frame carrying client traffic is to bemapped within the payload of a carrier frame, a plurality of first levelGFP frames are mapped to the payload area of a second level GFP frame.This second-level GFP frame is then mapped to the payload area of thecarrier network frame by mapper 18 shown in FIG. 8A.

The fragmentation process also enables very large client signals to befragmented and mapped into a plurality of GFP frame payloads where eachGFP frame payload is then mapped to a carrier frame payload area. Inthis way, a single client frame is fragmented into a plurality ofcarrier frames suitable for transmission over the carrier network.

Regardless of whether a GFP frame hierarchy according to the inventionhas one or more levels, it is the lowest level of the GFP framehierarchy which is mapped to the payload area of the carrier frame (step50) by mapper 18 for transmission out over the carrier network bytransmitter 20.

One specific embodiment of the invention uses a two-level hierarchy ofGFP frames to provide an adaptation layer for a carrier Ethernet networkwhich enables a plurality of different client signal payloads to becarried within a carrier Ethernet frame payload area. This assumes thatthe client signal payloads can be routed along the same path over theEthernet carrier network so that they can be multiplexed together withinthe same Ethernet frame payload. Each of the highest level of GFP frameswithin a carrier Ethernet frame is able to carry a client signalconforming to a different communications type and/or from a differentclient where the different client signals are able to be transportedwithin the same Ethernet frame. This can enable more efficienttransportation of small payload signals such as VoIP over Ethernet forexample. The client networks could use the Ethernet communicationsprotocol. In one embodiment, the Ethernet communications protocol is aconnection-oriented protocol which enables an Ethernet Wide Area Networkcarrier service to be provided.

In FIG. 8B, node 22 functions as a point of encapsulation for clienttraffic. Those of ordinary skill in the art will appreciate that one orcomponents providing the functionality comprising an encapsulating node10 may also be used to provide functionality for a de-encapsulatingnode, for example, the same network apparatus may both encapsulate andde-encapsulate client traffic into a GFP adaptation layer into carriertraffic and vice versa.

In FIG. 8B, receiver 24 of node 22 receives a carrier traffic signal(step 60). Each frame of the received carrier signal is processed bydata processor 26 to determine if its payload comprises data conformingto the GFP communications protocol (step 61 of FIG. 8B). For example, inan embodiment where the carrier network utilises an Ethernetcommunications protocol, the header of each carrier Ethernet frame isprocessed to determine if the value in the Ethertype header fieldindicates the payload area contains data conforming to the GFPcommunications protocol. If so, a GFP frame is then de-encapsulated fromthe carrier frame payload (step 62) by de-mapper 28.

The GFP frame is then processed by data processor 26 to determine fromthe GFP header if the GFP frame contains any channel, sequence orfragmentation indicators (step 63) and the payload is de-extracted (step64).

The sequence indicator and one or more other GFP frame headers may thenbe processed to determine if the sequence number indicates the GFP framecontains the “nth” payload segment or “nth” client frame in a sequenceof 1 to n GFP frame payloads (step 68) and if a channel indicator ispresent, the channel to which the client signal data was derived.

If the payload of the de-encapsulated frame is the nth segment in asequence of n segments, then a check is performed to see if all of theother 1 to n−1 GFP frame payloads have already been received and arestored in buffer 30, if so the other n−1 payloads are retrieved frombuffer 30 (or other suitable memory means) (step 70). If not all of theother frame payloads required to reassemble the original sequence ordata structure have been received then the payload of the nth GFP frameis also stored (step 72) in buffer 30.

If the received frame is not the nth frame, a check is performed to seeif the nth frame has already been stored (step 66) in buffer 30, if not,the received frame is stored (step 72) in buffer 30.

If the payload of the nth frame has already been received, a furthercheck is performed to see if the payloads of all n−1 frames required torestore the data sequence/structure have now been received (step 70). Ifso, all previously stored payloads (step 74) are retrieved. Theretrieved payloads are then reassembled (step 76) by data assembler 32.If the reassembled data also forms a GFP frame, a check is performed tosee if its payload data is also GFP (step 61). If so, the processre-iterates until finally the reassembled data forms a client layer PDU(step 78).

Once a client PDU has been recovered from the carrier network signal itcan be transmitted out over a client network by client traffictransmitter 34.

Where a sequence indicator is present in the extension field of the GFPheader, it indicates that the node receiving that GFP frame needs torestore a predetermined sequence of GFP frame payloads to recover theoriginal client signal integrity. This either comprises reassembling theoriginal sequence of client signal frames which were mapped into GFP byan encapsulating node 10 or reassembling data to form another PDU(either GFP or of the client signal if the client signal was fragmentedat the encapsulating node or an intermediate node).

In FIG. 8B, if a sequence indicator is found but the payload is notformed from fragmenting a client layer PDU, the de-encapsulated contentsneed only to be buffered sufficiently to restore the original sequenceof PDUs forming the client signal as shown by the dashed line betweensteps 68 and 76 in FIG. 8B.

Where a channel indicator is present in the extension header of the GFPframe being de-encapsulated, the data assembler restores the payloadderived from that frame to the client channel from which it was derived(and if fragmented ensures that all fragments are reassembled into aclient PDU which is restored to the correct client signal channel). Eachclient channel signal is then forwarded to the transmitter 34 foronwards transmission in the appropriate manner (which may involvedifferent communications protocols in some embodiments of theinvention).

A client signal can be fragmented either directly into GFP or indirectlyby mapping the client signal in its entirety into a GFP frame and thenfragmenting the GFP frame.

Those of ordinary skill in the art will be aware of modifications andfunctional equivalents to those described in the above embodiments ofthe invention, and the scope of the claims should be interpreted toinclude such variations to the described embodiments where they areapparent to one of ordinary skill in the art.

Although explicit reference is made hereinabove to the GFPcommunications protocol, any communications protocol which providesequivalent functionality essential to implement the claimed inventionmay be used whether a standard variant or not of a current standard GFPcommunications protocol.

What is claimed is:
 1. A machine-implemented method of client datatransportation in a carrier Ethernet communications system, the methodcomprising use of at least one data processor to perform method stepscomprising: receiving, at a node, a generic framing procedurecommunications protocol frame carrying as payload a type ofcommunications protocol client data; and mapping, using the dataprocessor, the received generic framing procedure frame carrying saidclient data to the payload area of one or more carrier generic framingprocedure communications protocol frames; wherein data comprising aplurality of said carrier generic framing procedure communicationsprotocol frames is encapsulated within the payload area of a singleEthernet protocol data unit for transport in said carrier Ethernetcommunications system, whereby the hierarchical encapsulation of saidgeneric framing procedure frames provides an adaptation layer for clientdata conforming to a plurality of different communications protocols fortransport over said carrier Ethernet communications system.
 2. A methodas claimed in claim 1, wherein the carrier Ethernet protocol comprises aconnection-oriented Ethernet communications protocol.
 3. A method asclaimed in claim 1, wherein a generic framing procedure frame which ismapped to the payload area of the carrier Ethernet protocol data unitcomprises a header having an extension field arranged to indicate thefragmentation status of its payload and the sequence number of a payloadfragment.
 4. A method as claimed in claim 1, wherein a generic framingprocedure frame which is mapped to the payload area of the Ethernetprotocol data unit comprises a header having an extension field arrangedto indicate a channel identity of its payload.
 5. A method as claimed inclaim 4, implemented on a node in a Ethernet carrier communicationsnetwork arranged to provide an aggregation service to multiplex clienttraffic received from lower rate ports to a carrier network accessedthrough one or more higher rate ports of the node, the methodcomprising: receiving client traffic conforming to one or morecommunications protocols from a plurality of lower rate ports, mappingthe client traffic into the payload area of one or more of said clientgeneric framing procedure communications protocol frames; wherein eachclient generic framing procedure frame is mapped to the payload area ofa generic framing procedure communications protocol carrier frame havingan extension field indicating the channel number of its payload, andeach carrier generic framing procedure frame is mapped to the payloadarea of an Ethernet protocol data unit of the Ethernet carrier network.6. A method of restoring client data which has been adapted fortransportation in an Ethernet carrier communications system using themethod as claimed in claim 1, the method of restoring comprising:processing at a node in said communications system a received carrierEthernet frame to determine if its payload comprises a frame conformingto a generic framing procedure communications protocol; and if thepayload is a generic framing procedure communications protocol frame: i)de-encapsulating the payload; ii) processing the header fields of thede-encapsulated generic framing procedure frame; and iii) determining ifthe payload further comprises one or more generic framing procedurecommunications protocol frames, and if so, repeating the above steps i)to iii).
 7. A method as claimed in claim 6, further comprising:processing one or more extension fields of a header of eachde-encapsulated generic framing procedure frame to determine if achannel identifier is present indicating the channel identity of theclient signal from which the payload is derived.
 8. Apparatus comprisingone or more components arranged to implement steps in a method asclaimed in claim
 1. 9. A method as claimed in claim 1, wherein saidadaptation layer enables client data comprising a plurality of differentcommunications protocols to be encapsulated within the payload of asingle Ethernet frame.
 10. An apparatus for adapting client data fortransportation in a carrier Ethernet communications system, theapparatus comprising: a node configured to receive a generic framingprocedure communications protocol frame carrying as payload a type ofcommunications protocol client data; and a processor configured to mapthe received generic framing procedure frame carrying said client datato the payload area of one or more carrier generic framing procedurecommunications protocol frames; wherein data comprising a plurality ofsaid carrier generic framing procedure communications protocol frames isencapsulated within the payload area of a single Ethernet protocol dataunit for transport in said carrier Ethernet communications system,whereby the hierarchical encapsulation of said generic framing procedureframes provides an adaptation layer for client data conforming to aplurality of different communications protocols for transport over saidcarrier Ethernet communications system.
 11. The apparatus as claimed inclaim 10, wherein the carrier Ethernet protocol comprises aconnection-oriented Ethernet communications protocol.
 12. The apparatusas claimed in claim 10, wherein a generic framing procedure frame whichis mapped to the payload area of the carrier Ethernet protocol data unitcomprises a header having an extension field arranged to indicate thefragmentation status of its payload and the sequence number of a payloadfragment.
 13. The apparatus as claimed in claim 10, wherein a genericframing procedure frame which is mapped to the payload area of theEthernet protocol data unit comprises a header having an extension fieldarranged to indicate a channel identity of its payload.
 14. Theapparatus as claimed in claim 10, wherein said adaptation layer enablesclient data comprising a plurality of different communications protocolsto be encapsulated within the payload of a single Ethernet frame.